To facilitate the understanding and description of the present invention as well as the knowledge of the problems behind the invention, here follows a description of both the basic construction and the function of floorboards with reference to FIG. 1 in the accompanying drawings.
FIGS. 1a-1d show according to known art, how laminate flooring is produced. A floor element 3, FIGS. 1a-b, in the form of a large laminated board, is sawn into several individual floor panels 2, FIG. 1c, which are then further machined to floorboards 1, 1′, FIG. 1d. The floor panels are individually machined along their edges to floorboards with mechanical joint systems on the edges. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and belts or similar, so that the floor panel can be moved at high speed and with great accuracy such that it passes a number of milling motors, which are provided with diamond cutting tools or metal cutting tools and which machine the edge of the floor panel and forms the joint system.
A floorboard 1, 1′, FIG. 1d, having a mechanical joint system has active locking surfaces in the tongue 10 (the tongue side of the floorboard 1′) and the tongue groove 9 (the groove side of the floorboard 1). Laminate flooring and wood veneer flooring are usually composed of a body 30 including a 6-12 mm fiberboard, a 0.1-0.8 mm thick top surface layer 31 and a 0.1-0.6 mm thick lower balancing layer 32. The top surface layer 31 provides appearance and durability to the floorboards. The body provides stability and the balancing layer keeps the board leveled when the relative humidity (RH) varies during the year. The RH can vary between 15% and 90%.
Conventional floorboards with a wood surface were previously usually joined by means of glued tongue-and-groove joints. The edges were often formed with bevels in order to eliminate tight tolerances.
In addition to such traditional floors, floorboards have been developed in recent years, which do not require the use of glue but which are instead joined mechanically by means of so-called mechanical joint systems. These systems comprise locking means, which lock the boards horizontally and vertically. The mechanical joint systems can be formed by machining the core 30 of the board 1, 1′. Alternatively, parts of the joint system can be made of a separate material, which is integrated with the floorboard. The floorboards are joined, i.e. interconnected or locked together in a floating manner, by various combinations of angling, snapping, insertion along the joint edge and by fold down methods using joint systems comprising separate displaceable tongues generally factory inserted in a groove at the short edges.
Such floors can be formed with tight tolerances. Bevels are therefore mainly used to obtain decorative properties. A laminate floor panel with a thin surface layer can be formed with beveled edges and then looks like a solid wood plank.
The advantage of a floating flooring which is not connected to a sub floor with, for example, nails or glue, is that a change in shape due to different degrees of relative humidity RH can occur concealed under basemouldings and the floorboards can, although they swell and shrink, be joined without visible joint gaps. Installation can, especially by using mechanical joint systems, be laid quickly and easily. The drawback is that the continuous floor surface must as a rule be limited even in the cases where the floor comprises of relatively dimensionally stable floorboards, such as laminate floor with a fiberboard core or wooden floors composed of several layers with different fibre directions. The reason is that such floors as a rule shrink and swell as the RH varies.
A solution for large floor surfaces is to divide the large surface into smaller surfaces with expansion strips. Without such a division, it is a risk that the floor when shrinking will change in shape so that it will no longer be covered by basemouldings. Also the load on the joint system will be great since great loads must be transferred when a large continuous surface is moving. The load will be particularly great in passages between different rooms. Examples of expansion strips are joint profiles that are generally aluminum or plastic section fixed on the floor surface between two separate floor units. They collect dirt, give an unwanted appearance and are rather expensive. Due to these limitations on maximum floor surfaces, laminate floorings have only reached a small market share in commercial applications such as hotels, airports, and large shopping areas. More unstable floors, such as wooden floors, may exhibit still greater changes in shape. The factors that above all affect the change in shape of homogenous wooden floors are fibre direction and the kind of wood. A homogenous oak floor is very stable along the fibre direction, i.e. in the longitudinal direction of the floorboard.
The advantage of gluing/nailing to the subfloor is that large continuous floor surfaces can be provided without expansion joint profiles and the floor can take up great loads. This method of installation involving attachment to the subfloor has, however, a number of considerable drawbacks. The main drawbacks are costly installation and that as the floorboards shrink, a visible joint gap arises between the boards.
In view of the cited documents there is still a need of improving a floating floor without the above drawbacks, in particular a floating floor which a) may have a large continuous surface without expansion joint profiles, b) may have a non-visible joint gap, and c) may have a bevel with the same visual effects as for a more expensive wood based floorboard. There is still a need of improving a method for producing such a floating floor, without the above drawbacks in particular a manufacturing method which may be less complex, thereby speeding up the manufacturing and decreasing the cost.